These days, databases are used to store a very large amount of data originating from many sources. It is known that these data are stored in tables each comprising several fields, these tables being defined by the data model. Relationships are established between the fields of various tables and recorded in the database.
To obtain the data sought in a database, using a query language for interrogating the database is known. Thus, by using a query the content of some fields in some tables can be obtained, according to predetermined criteria which are commonly defined in filters.
SQL is a commonly used language for interrogating a database. The syntax of this language allows data from many sources to be retrieved, filtered and recompiled according to search criteria and relationships between the tables, particularly to order said data in a two-dimensional array.
SQL comprises multiple keywords to, perform one or more of these actions for the same query.
It is an extremely powerful language but its use is limited to experienced users with a very good command of the language. In particular, to formulate a query using SQL, the fields for which data are sought, the tables containing these fields, the filters used and the relationships between the tables containing the various fields, as defined in the database, must be specified.